There are various conventional combustion processes for internal combustion engines. The present invention is directed to controlling and regulating the so-called HCCI combustion process for gasoline engines (homogeneous charge compression ignition, also referred to as gasoline HCCI or controlled auto ignition, CAI). HCCI refers to a lean combustion process which has the goal of demonstrating a significant fuel consumption reduction of 10%-15% in the motor vehicle (due to dethrottling of the engine operation and a thermodynamically advantageous combustion) without significant untreated nitrogen oxide emissions (the three-way-catalytic converter does not have a nitrogen-reducing effect during lean operation), and thus also not having to accept additional costs for exhaust aftertreatment.
Since gasoline and the compression ratio of a gasoline engine are designed in such a way that auto ignitions (knocking) are avoided to the greatest possible extent, the thermal energy which is necessary for the HCCI process must be provided by a different source. This may take place in various ways such as retention or back-suction of the hot internal residual gas or heating of the fresh air, for example.
Carrying out an HCCI combustion process requires a number of functionalities of the internal combustion engine, in particular a direct injection, a (partially) variable valve gear (e.g., phase variability and two-point lift) as well as feedback from the combustion (e.g., combustion chamber pressure, structure-borne noise, ion current, high-resolution rotational speed signal, etc.).
An important aspect in this context is the engine control, which must be expanded by special functions both for the steady-state control and regulation of the HCCI combustion and for the dynamic control and regulation (load change and switching between operating modes). The task of the steady-state control and regulation is to maintain/set the operating point, the cylinder equalization, and the compensation for environmental influences. The task of the dynamic control and regulation is to make the fastest possible load changes possible and to not allow knocking or misfiring combustions.
The HCCI combustion process requires a careful coordination between the control and regulation of the combustion itself and the air system states in the intake manifold, in order to simultaneously achieve the described consumption advantages and acceptable pollutant emissions.
A corresponding control procedure is described in the application “Method for controlling an HCCI combustion in a reactor of an internal combustion engine” which was filed by the applicant on the same day and to whose entire content reference is made and whose content is regarded here as disclosed. In this application, a control method for an HCCI combustion is described which may be used as the starting point of the present invention and upon which the present invention may build for optimization. In particular, during the dynamic HCCI operation (e.g., load change) suboptimal operation phases temporarily occur, since the control actions are each subject to a different delay behavior for hardware reasons. This is due to the fact, among other things, that the air system states follow the intake manifold dynamics and the phase controllers are subject to dead times and are rate-limiting controlled.
Similar problems arise when switching between processes, for example from an HCCI process to an SI process (spark ignition) and vice versa. A corresponding switchover method is described in the application “Method for switching between an HCCI combustion and an SI combustion in a reactor of an internal combustion engine” which was filed by the applicant on the same day and to whose entire content reference is made and whose content is regarded here as disclosed. In this application, a switchover method is described which may be used as the starting point of the present invention and upon which the present invention may build for optimization. During an HCCI to SI transition, it is namely necessary, on the one hand, to eject the internal residual gas as quickly as possible, ideally within one ejection sequence, and, on the other hand, it must be prevented that the air/fuel mixture becomes excessively lean when the combustion chamber volume, which becomes available due to the residual gas ejection, is filled with fresh air.
It is thus desirable to control the air system states in the intake manifold so that possibly no misfiring or knocking combustions occur in the reactor of the internal combustion engine.